I have these on my vehicle and would like to know some suggestions to try for troubleshooting. The "fuel to lean" description in my service manual is just a little too vague for me to handle. Any suggestions?

Check for vacuum leaks. Look for cracked hoses and spray starter fluid (ether) around the intake manifold.Check the tubing between the MAF sensor and the manifold.Clean the MAF sensor.http://www.obd-codes.com/p0171

Is it possible that I have a hose leak around the gas tank itself? Some months before I really started to notice the mileage issue and well before the codes came on I got a strong wiff of gas for a couple of days after each fillup. Only once did I have spillage from underneath, so I didn't really worry too much. Is there a hose or series of hoses that connects the tank and the engine in some way for vapor or intake purposes?

This is really more of a strong hunch than evidence. If this is correct, how much trouble is it to dop the tank? I have the luxury of time with this thing since I have another vehicle to use but have never done that before. Is it worth the hassle or should I just take it to somebody? Any ideas on the timeframe that I'm looking at for tank removal and reconnection?

As you suspect, there is a system for collecting gasoline vapors and shipping them to the engine. The vapors are stored in a charcoal canister and fed to the engine to burn rather than going to the atmosphere.

There is, however, a whole separate set of codes/sensors for that system so if that was your only problem you'd be very unlikely to get the codes reported.

It is the case, however, that the system does work by vacuum lines - the vapors are fed into the intake that way. Depending on the year (which you didn't mention) you might just be seeing two different problems from the same kind of course - really old, dried up vacuum tubing.

This stuff is really cheap and not hard to replace. There is a vacuum diagram on the underside of your hood. I've known people to just decide to replace all of their vacuum lines once these kinds of problems started to pop up.

The system described by Cigroller (the Evaporative Emissions System) is not causing the codes you posted. As Cigroller said, they have their own special fault codes. And a leak in that system cannot cause a lean bank.

However if you're smelling gas and had "spillage from underneath" you should get this looked at ASAP. Gas fumes are not safe.

I only had spillage once and I am a regular "top it all the way off" person. I can't really venture an explanation to why it only happened once. The smell is not peristent either really. Of course it's been around 20 degrees when I've filled it up lately so sticking around to sniff the tank hasn't been high on my priorities list.

I appreciate the help from everybody. I guess I will try some sensor cleaning and hose checking and then take it to the shop. It's got some kind of recall pending anyway. I just wanted to have as few issues for them to seize upon as possible since car repair is not something that I enjoy paying for. peace,